During foraging, animals decide how long to stay and harvest reward, and then abandon that site and travel with a certain speed to the next reward opportunity. One aspect of this behavior involves decision-making, while the other involves motor-control. A recent theory posits that control of decision-making and movements may be linked via a desire to maximize a single normative utility: the sum of all rewards acquired, minus all efforts expended, divided by time. If this is the case, then the history of rewards, and not just its immediate availability, should dictate how long one decides to stay and harvest reward, and how slowly one travels to the next opportunity. We tested this theory in a series of experiments in which humans used their hand to harvest tokens at a reward patch, and then used their arm to reach toward a subsequent opportunity. Following a history of poor rewards, people not only foraged for a longer period, but also moved slower to the next reward site. Thus, reward history had a consistent effect on both the decision-making process regarding when to abandon a reward site, and the motor control process regarding how fast to move to the next opportunity.

No abstract

No abstract

On any given day, we make countless reaching movements to objects around us. While such ubiquity may suggest uniformity, each movement is actually unique in the speed with which it is made. Some movements are slow, while others are fast. These variations in reach speed have long been known to be influenced by accuracy constraints; we slow down when accuracy demands are high. However, in other forms of movement like walking, metabolic cost is the primary determinant of movement speed. Here we ask, what is the role of metabolic cost in determining speed of reaching movements? First we systematically measure the effect of increasing mass on the metabolic cost of reaching across a range of movement speeds. Next, in a sequence of three experiments, we examine how added mass affects preferred movement speeds in a simple reaching task with increasing accuracy requirements. We find that mass consistently increased metabolic cost and led to slower movements. Yet, intriguingly, preferred reach speeds were faster than metabolically optimal. We then demonstrate how a cost function that, critically, considers both accuracy and metabolic cost can explain preferred movement speeds across the range of conditions tested. Together, these findings provide a unifying framework to explain the combined effects of metabolic cost and accuracy on movement speed, and also highlight the integral role metabolic cost plays in determining many forms of movement.

No abstract